Field of the Invention
The present invention relates to an image sensor driving apparatus and method, and a radiation imaging apparatus using the image sensor driving apparatus.
Description of the Related Art
Recently, in the field of digital X-ray imaging apparatuses, instead of an image intensifier, a large-area flat panel radiation imaging apparatus based on a 1× optical system using photoelectric conversion elements has been widely used for the purpose of increasing resolution, decreasing the volume of the imaging apparatus, and suppressing image distortion. As one of 1× optical system flat panel sensors used in radiation imaging apparatuses, there is available a large-area flat panel sensor formed by two-dimensionally joining photoelectric conversion elements formed on a silicon semiconductor wafer by a CMOS semiconductor manufacturing process.
Since photoelectric conversion elements are formed on a silicon semiconductor wafer, the size of a flat panel sensor is limited to the size of the silicon semiconductor wafer. Japanese Patent Laid-Open No. 2002-026302 has proposed a technique for implementing the imaging area of a large-area flat panel sensor which is larger in size than a silicon semiconductor wafer. This patent literature discloses a manufacturing method for forming a large-area flat panel sensor by tiling a plurality of rectangular semiconductor substrates which are rectangular image sensors obtained by cutting photoelectric conversion elements in the form of strips from a silicon semiconductor wafer.
In addition, Japanese Patent Laid-Open No. 2002-344809 discloses the circuit arrangement for each rectangular semiconductor substrate obtained by cutting out photoelectric conversion elements in the form of strips. On each of the rectangular semiconductor substrates cut out in the form of strips, vertical and horizontal shift registers acting as readout control circuits are arranged together with two-dimensionally arrayed photoelectric conversion elements. External terminals (electrode pads) are provided near the horizontal shift register. According to this arrangement, control signals and clock signals input from the external terminals control the vertical and horizontal shift registers on each rectangular semiconductor substrate to cause the respective shift registers to sequentially output the respective pixel arrays in synchronism with the clock signals.
It is, however, generally known that the above rectangular semiconductor substrates and semiconductor devices such as differential amplifiers and A/D converters generate shot noise, thermal noise, and 1/f (flicker) noise. In the semiconductors manufactured by a MOS process, 1/f noise is dominant in low-frequency regions. In a radiation imaging apparatus formed by tiling a plurality of rectangular semiconductor substrates, since such 1/f noise is superimposed on digital image data for each block having undergone A/D conversion by a plurality of A/D converters, block artifacts are generated.
If no 1/f noise is generated in a dark image obtained without any emission of radiation, the dark image having undergone FPN (fixed pattern noise) correction, a very flat image like that shown in FIG. 24A can be obtained. If, however, low-frequency 1/f noise is generated in rectangular semiconductor substrates, differential amplifiers, and A/D converters, a block artifact appears on an A/D converter basis, as shown in FIG. 24B. Since a radiation imaging apparatus is required to have a wide dynamic range, in particular, it is important for the readout circuit used in the radiation imaging apparatus to have low noise characteristics.